The new era of electronic products trend to light-weight, slim, and compact size, and are suitable for high-frequency transmission, therefore, the wiring for the circuit boards has developed towards higher density, and the selection for the circuit board materials has developed towards more stringent requirements. As the high frequency electronic components are engaged with the circuit boards, in order to maintain the transmission rate and keep the integrity of the transmission signals, the laminate materials for the circuit boards should have low dielectric constant (Dk) and dielectric loss tangent (also called dissipation factor, DO. At the same time, in order to maintain the normal operation function of the electronic components in a high-temperature and high-humidity environment, the circuit boards also should have the properties such as heat resistance, flame retardancy and low water absorption. Due to the excellent adhesion, heat resistance, and formability, the epoxy resins are widely applied in the electronic parts and components as well as the copper foil-coated laminate or sealing material of the electrical machinery. With respect to the safety for preventing from fire, the materials are required to have flame retardancy, generally the flame retardancy can be achieved by the epoxy resins having flame retardancy in combination with the additional flame retardants, for example, the epoxy resins are provided with flame retardancy by incorporating halogen, especially bromine therein, thus improving the reactivity of the epoxy groups. However, after a long-time use at a high temperature, the halides may occur dissociation, thus resulting in the risk of corrosion of the fine wires. Furthermore, after burning, the used waste electronic parts and components will generate the hazardous compounds such as halide and the like, and pollute the environment. In order to substitute for the abovementioned halide flame retardants, some studies apply phosphorus-containing compounds as flame retardants, for example adding phosphate ester (Taiwan Patent No. 1238846) or phosphorus red (Taiwan Patent No. 322507) into the epoxy resin composition. However, the phosphate ester will occur hydrolysis reaction to disassociate an acid from it, thus influencing its migration resistance; and although the phosphorus red has high flame retardancy, it is specified as a hazardous substance in the fire control law, as it can generate a minute amount of phosphine gas under a high temperature and humid environment.
At present, the environment-friendly halogen-free resin compositions, in order to achieve the flame retardancy of UL94 V-0, are generally added with phosphorus-containing flame retardants, wherein the DOPO compounds are preferred. However, the conventional DOPO compounds, as they have P—H bonds in their structures and have high activities with alkenes, epoxy bonds, and carbonyls, can react and form various derivatives. DOPO and its derivatives, as the molecular structures contain biphenyl ring and phenanthrene ring structures, particularly the side phosphorus groups are introduced in circular O═P—O bond, have higher thermal stability and chemical stability, and better flame retardancy as compared with the general acyclic organophosphate. DOPO and its derivatives can be used as reaction type and addition type flame retardants, the synthetized flame retardants have no halogen, no smoke, no toxicity, no migration, and long-lasting flame retardant property. As the DOPO compounds containing hydroxyls (such as DOPO-HQ from Nu Tech Fine Chemical Co. Ltd.), due to their hydroxyls, can react and bond with other resins, and the presence of hydroxyls will in turn result in adverse effects on the dielectric constant and dielectric loss tangent (the excessive high Dk and Df values), the DOPO compounds containing hydroxyls are not suitable to be added in the low dielectric resin composition.
With respect to the electrical properties of the copper foil-coated laminates and printed circuit boards, those to be mainly contemplated comprise dielectric constant and dielectric loss tangent of the material. In general, as the signal transmission speed of the laminate is inversely proportional to the square root of the dielectric constant of the laminate material, the lower dielectric constant of the laminate material is generally better; on the other hand, as the lower dielectric loss tangent represents the lower signal transmission loss, the material having lower dielectric loss tangent can provide better transmission quality.
Therefore, how to develop a material still having low dielectric constant and low dielectric loss tangent which are measured at 10 GHz, and apply it in manufacturing a high frequency printed circuit board, are the problems to be solved by the printed circuit board material supplies at present.